Soil-borne pathogenic fungi cause a great deal of damage to seedling crops. These parasites cause damping-off, root-rot, crown-rot, and neck-rot in a wide variety of host plants. The most common pathogenic fungi of this sort are the Rhizoctonia, Pythium, Fusarium, Phytophotora and Sclerotia species. Rhizoctonia, Pythium and Sclerotia species have extraordinarily wide host ranges and are capable of attacking many common commercial crops, such as beans, tomatoes, cotton, peanuts, potatoes, lettuce, flowers and others.
Currently, chemical methods are employed to control these fungi. However, chemicals are potentially hazardous to public health and the environment. They can change the ecosystem and thereby upset the microenvironment of the plants. Furthermore, chemical fungicides are relatively expensive. An alternative to the use of chemicals is the use of biological control agents, which are naturally found in the ecosystem.
Certain species of Trichoderma have been found to possess antagonistic and hyperparasitic properties. A comprehensive review on this is found in Ann Rev. Microbiol. 1981, Vol. 35, pages 459-463. It was thus found that Trichoderma spp. can effectively reduce diseases caused by some soil-borne plant pathogens. The species T. harzianum, T. hamatum, and T. viride are species of Trichoderma which have been demonstrated to have fungicidal activity against Sclerotium rolfsii, Rhizoctonia Solani Pythium spp, and Fusarium spp. One serious handicap to commercialization of suitable strains of these fungi for antifungal applications is the lack of a practical large scale production method for these organisms.
The most common method for growing Trichoderma is on solid media which is too expensive and impractical for commercial adaptation. On the other hand, propagation of Trichoderma by a large scale submerged culture process would be most suitable for commercial adaptation, but such a commercial process is not known.
Methods for growing Trichoderma in liquid media, i.e. submerged culture, have been disclosed in the literature. These methods are laboratory processes and do not produce the high yield of spores on a large scale and in a reasonable amount of time as required to make them commercially viable. Elad, Y., et al., (1982) Can. J. Microbiol 28: 719-725; Vezina, C., et al. (1965) Mycologia 57: 722. Thus, for example, Aube and Gagnon, (1969) Can. J. Mcrobiol., 15:703-705 studied the growth and sporulation of several isolates of T. viride in liquid cultures. The method involved growing the organisms for a week in the dark at 20.degree. C. as a stationary culture. Zuber and Turian, (1981) Trans.Br.Mycol.Soc. 76(3), pg. 433-440 disclose microcycle conidiation of T. harzianum in liquid cultures and several growth media are disclosed for this method.